gouri - 3:12 am on Nov 8, 2012 (gmt 0)
We haven't made any significant changes to the site in months, except removing a single link to an offsite page from a navigation bar from about 50% of the pages.
Can you describe the link that you removed from the navigation bar? Was it a keyword phrase that the page that you linked to is trying to rank for? Was it a url link?